A plasma display panel (PDP) is a type of gas discharge panel that achieves image display by using UV light from gas discharges to excite phosphors to emit visible light. PDPs can be classified into alternating current (AC) and direct current (DC) types on the basis of how discharges are formed, with the AC type being more typical because of its superiority in terms of luminance, luminous efficiency and device life.
In an AC PDP, two thin glass panel surfaces having a plurality of electrodes (display & address electrodes) disposed thereon and dielectric layers covering the electrodes oppose each other via a plurality of barrier ribs. Phosphor layers are disposed between adjacent barrier ribs and a discharge gas is enclosed between the two glass panels, with a plurality of discharge cells (subpixels) formed in a matrix. A protective layer (film) is formed on a surface of the dielectric layer covering the display electrodes. The protective layer preferably provides for significant reductions in both a firing voltage Vf and any discharge-to-discharge variability between the cells. A magnesium oxide (MgO) crystal film is ideal as the protective layer, given the excellent spatter resistance and large secondary electron emission coefficient of MgO.
Phosphor luminescence in a PDP is achieved by applying suitable voltages to the plurality of electrodes based on a so-called intrafield time division grayscale display scheme to generate discharges within the discharge gas when the PDP is driven. Specifically, when the PDP is driven each display frame is firstly divided into a plurality of subframes and each subframe is further divided into a plurality of time periods. In each subframe, the wall charge over the entire screen is firstly reset (reset period), before selectively generating an address discharge to store wall charge in discharge cells for turning ON (address period), and sustaining the discharge for a fixed period of time by applying an AC voltage (sustain voltage) simultaneously to all of the discharge cells (sustain period). Since the discharges are based on probability, variability generally exists in the rate (“discharge probability”) at which discharges occur in individual discharge cell. Thus the discharge probability of the address discharge, for example, can be raised proportionately to the width of the applied pulse.
A typical PDP structure is disclosed, for example, in Japanese Patent Application Publication No. 09-92133.
Here, an MgO protective layer is used to realize low voltage operation, although the operating voltage still is high in comparison to LCD display devices, for example. A high voltage transistor is thus needed in the drive IC, this being one of the factors hiking up the cost of PDPs. This has lead to present demands to move away from using costly high voltage transistors while at the same time reducing the firing voltage Vf in order to reduce the energy consumption of PDPs.
Apart from thin film techniques such as vacuum deposition (VD), electron beam deposition (EBD) and sputtering, the MgO film that constitutes the protective layer can be deposited by printing (thick film technique) an organic material (MgO precursor). With the printing technique, as disclosed in Japanese Patent Application Publication No. 04-10330, the protective layer is formed by mixing an liquid organic material with a glass material, spin coating the mixture on a glass panel surface and baking the applied mixture at around 600° C. to crystallized the MgO. Printing is relatively simple and low cost in comparison to the VD, EBD and sputtering techniques, and is also an excellent choice in terms of throughput since a vacuum process is not required.
However, with protective layers formed using a thick film technique, discharge-to-discharge variability between the discharge cells readily occurs when the PDP is driven, despite there being only slight gains in reduced firing voltage Vf over protective layers formed by thin film techniques using a vacuum process. Discharge variability is a problem that needs addressing since it results in so-called “black noise”, possibly making it difficult to achieve satisfactory image display performance. Black noise is when selected discharge cells fail to turn ON, increasing the likelihood of a demarcation arising between illuminated and non-illuminated areas on the screen. Black noise is thought to arise either from failed or weak address discharges, since it is disparate cells rather than all selected cells a single line (i.e. longitudinal direction of the display electrodes) or a single column (i.e. longitudinal direction of adjacent barrier ribs) that fail to turn ON. Electrons emitted from the MgO are known to play a major part in this.
Since black noise occurs readily with protective layers formed using MgO having few oxygen deficient regions (i.e. oxygen rich MgO) with thin as well as thick film techniques, an immediate solution to the problem is sought with respect to both techniques.
The present invention, devised in view of the above problems, aims to provide a PDP capable of excellent image display performance by efficiently reducing both the firing voltage Vf and discharge-to-discharge variability while remaining relatively low cost, and to a manufacturing method for the same.